Molybdenum based oxidation catalysts

ABSTRACT

This invention concerns catalysts comprising a molybdenum compound of formula I, II, III, IV or V  
     I V q MoA y O z    
     II NiMo x B y O z′   
     III VNi w Mo x C y′ O z″   
     IV CoNi w Mo x D y O z′″   
     V VNi w Co r Mo x E y O z″″   
     wherein: A is at least one cation selected from the group consisting of cations of: Cr, Sb, Co, Ce and Pb; B is at least one cation selected from the group consisting of cations of: Sb, Al and W; C is at least one cation selected from the group consisting of cations of: Fe, Zn, Al, Sb, Bi, W, Li, Ba, Nb and Sn; D is at least one cation selected from the group consisting of cations of: Ba, Mn, Al, Sb, Sn, and W; E is at least one cation selected from the group consisting of cations of: Fe, Ca, Mn, Sr, Eu, La, Zr, Ga, Sn and Pb; q, r, w, x and y are each independently a number from 0.1 to 10 and y′ is a number from 0 to 10, z, z′, z″, z′″, and z″″ are determined using the amounts and oxidation states of all cations present in each formula. These catalysts can be used in C 4  oxidation processes, especially butane oxidation processes.

FIELD OF THE INVENTION

[0001] This invention relates to compounds comprising molybdenum, oxygenand certain cations, and the use of these compounds as catalysts in C₄oxidation processes, especially butane oxidation processes.

TECHNICAL BACKGROUND

[0002] Oxidative organic processes are widely used in industrialoperations. One commercially valuable process involves the oxidation ofbutane to maleic anhydride. Maleic anhydride is used as a raw materialfor products ranging from agricultural chemicals, paints, paper sizingand food additives to synthetic resins. To fill the high demand for thisvaluable chemical, a variety of commercial processes have beendeveloped.

[0003] One important route to maleic anhydride involves the vapor phaseoxidation of n-butane over a vanadium/phosphorus oxide (VPO) catalyst.The reaction step involves oxidation of n-butane with air (oxygen) toform maleic anhydride, carbon oxides, water and smaller amounts ofpartially oxidized by-products. Typically, the process is carried out infixed-bed reactors, fluid-bed reactors, or more recently inrecirculating solids reactors having two reaction zones in which twoseparate reactions take place with a catalyst (the solid) circulatingbetween the two reaction zones and taking part in reactions in bothzones.

[0004] A number of non-VPO catalysts have been reported in theliterature. Zazhigalov, V. A. et al., in an article entitled “Oxidationof n-butane on Vanadium Molybdenum-Oxide Catalysts”, Inst. Fiz. Khim.im. Pisarzhevskogo, Kiev USSR Neftekhimiya (1977), 17 (2),268-73describe the activity of V₂O₅-MoO₃ catalysts in butane oxidation aspassing through a maximum at 25% MoO₃, and that a certain catalyticstructure consisting of, V⁴⁺, V⁵⁺ and Mo⁶⁺ ions correspond to theirpreferred catalyst composition. These results obtained at 500-600° C.indicate low catalyst activity at normal operating temperatures.

[0005] Mazzochia, C. R. et al., in “Selective Oxidation of Butane in thePresence of NiO-MoO₃ catalysts”; An. Quim. Ser. A 79, no. 1108-113(1983) disclose nickel molybdate catalysts prepared bycoprecipitation that exhibit low hydrocarbon conversions. At 475° C.,19% conversion of n-butane was noted with low selectivities to maleicanhydride.

[0006] Umit Ozkan and G. L. Schrader, in “Synthesis, Characterizationand catalytic behaviour of cobalt molybdates for 1-butene oxidation tomaleic anhydride”, Applied Catalysis, 23 (1986) 327-338 disclose the useof cobalt molybdate for the oxidation of 1-butene.

[0007] In spite of the progress in catalyst and process development overthe years, a need still remains for improved non-VPO catalysts useful inthe oxidation of C4 hydrocarbons, particularly n-butane, to maleicanhydride and especially catalysts which are active at lowertemperatures and have shorter contact times; and it is to that end thatthe present invention is directed.

SUMMARY OF THE INVENTION

[0008] The present invention provides a catalyst, comprising amolybdenum compound of formula I, II, III, IV or V:

[0009] I V_(q)MoA_(y)O_(z)

[0010] II NiMo_(x)B_(y)O_(z′)

[0011] III VNi_(w)Mo_(x)C_(y′)O_(z″)

[0012] IV CoNi_(w)Mo_(x)D_(y)O_(z′″)

[0013] V VNi_(w)CO_(r)Mo_(x)E_(y)O_(z″″)

[0014] wherein:

[0015] q is a number from 0.1 to 10;

[0016] r is a number from 0.1 to 10;

[0017] w is a number from 0.1 to 10;

[0018] x is a number from 0.1 to 10;

[0019] y is a number from 0.1 to 10;

[0020] y is a number from 0 to 10,

[0021] A is at least one cation selected from the group consisting ofcations of: Cr, Sb, Co, Ce and Pb;

[0022] B is at least one cation selected from the group consisting ofcations of: Sb, Al and W;

[0023] C is at least one cation selected from the group consisting ofcations of: Fe, Zn, Al, Sb, Bi, W, Li, Ba, Nb and Sn;

[0024] D is at least one cation selected from the group consisting ofcations of: Ba, Mn, Al, Sb, Sn, and W;

[0025] E is at least one cation selected from the group consisting ofcations of: Fe, Ca, Mn, Sr, Eu, La, Zr, Ga, Sn and Pb; and

[0026] z, z′, z″, z′″, and z″″ are determined using the amounts andoxidation states of all cations present in each formula according to thefollowing equations:

[0027] z=((q times oxidation state of V)+(1 times oxidation state ofMo)+(y times oxidation state of A)) divided by 2 (oxidation state ofoxygen);

[0028] z′=((1 times oxidation state of Ni)+(x times oxidation state ofMo)+(y times oxidation state of B)) divided by 2 (oxidation state ofoxygen);

[0029] z″=((1 times oxidation state of V)+(w times the oxidation stateof Ni)+(x times oxidation state of Mo)+(y′ times oxidation state of C))divided by 2 (oxidation state of oxygen);

[0030] z′″=((1 times oxidation state of Co)+(w times the oxidation stateof Ni)+(x times oxidation state of Mo)+(y′ times oxidation state of D))divided by 2 (oxidation state of oxygen); and

[0031] z″″=((1 times oxidation state of V)+(w times the oxidation stateof Ni)+(r times the oxidation state of Co)+(x times oxidation state ofMo)+(y′ times oxidation state of E)) divided by 2 (oxidation state ofoxygen).

[0032] The present invention also provides a process for the oxidationof a C4 hydrocarbon to maleic anhydride, comprising: contacting the C4hydrocarbon with a source of oxygen in the presence of a catalyticamount of a molybdenum catalyst comprising a compound of formula I, II,III or V, as defined above, to yield maleic anhydride.

[0033] The present invention further provides a process for theoxidation of n-butane to maleic anhydride, comprising: contactingn-butane with a source of oxygen in the presence of a catalytic amountof a molybdenum catalyst comprising a compound of formula IV, as definedabove, wherein the molybdenum catalyst is in a bulk state, to yieldmaleic anhydride.

[0034] The present invention also provides a process for the oxidationof n-butane to maleic anhydride, comprising: contacting n-butane with asource of oxygen in the presence of a catalytic amount of a catalystcomprising a molybdenum compound of formula VI or VII in a crystalline,active phase

[0035] VI V₉Mo₆O₄₀

[0036] VII V₂MoO₈

[0037] to yield maleic anhydride.

[0038] The present invention also provides a process for the preparationof a molybdenum compound comprising a crystalline oxide of formula I,II, III, IV or V, as described above, comprising the steps of:contacting at least one compound having a cation of the molybdenumcompound with at least one cation containing compound for each of theother cations of the molybdenum compound in a solution comprising waterto form a resultant solution or colloid; freezing the resultant solutionor colloid to form a frozen material, freeze drying the frozen material;and heating the dried frozen material to yield the molybdenum compoundof formula I, II, III, IV, V, VI or VII.

DETAILED DESCRIPTION OF THE INVENTION

[0039] Multicomponent catalyst systems have been identified hereinwherein the presence of molybdenum in combination with other particularcations show a significant beneficial effect on catalyst performancescompared with many non-VPO catalysts reported in the literature forn-butane oxidation. These new multicomponent catalysts of the presentinvention comprise a molybdenum compound of formula I, II, III, IV or V:

[0040] I V_(q)MoA_(y)O_(z)

[0041] II NiMo_(x)B_(y)O_(z′)

[0042] III VNi_(w)Mo_(x)C_(y′)O_(z″)

[0043] IV CoNi_(w)Mo_(x)D_(y)O_(z′″)

[0044] V VNi_(w)Co_(r)Mo_(x)E_(y)O_(z″″)

[0045] wherein: q is a number from 0. 1 to 10; r is a number from 0.1 to10; w is a number from 0.1 to 10; x is a number from 0.1 to 10; y is anumber from 0.1 to 10; and y is a number from 0 to 10.

[0046] A is at least one cation selected from the group consisting ofcations of: Cr, Sb, Co, Ce and Pb. A is preferably Sb, and a preferredcompound of formula I is V₁Mo₁Sb₁O_(z). B is at least one cationselected from the group consisting of cations of: Sb, Al and W. B ispreferably Sb, and a preferred compound of formula II isNi₁Mo_(2.3)Sb₁O_(z′). C is at least one cation selected from the groupconsisting of cations of: Fe, Zn, Al, Sb, Bi, W, Li, Ba, Nb and Sn. C ispreferably Bi, or Nb and Sn, and preferred compounds of formula III areV₁Mo_(2.3)Ni₁Bi₁O_(z″), and V₁Mo_(2.3)Ni₁Nb₁Sn₁O_(z″). D is at least onecation selected from the group consisting of cations of: Ba, Mn, Mo, Al,Sb, Sn, and W. D is preferably Sn or W, and preferred compounds offormula IV are Co_(0.5)Ni_(0.5)Mo₃Sn_(0.5)O_(z′″) andMo₃Co_(0.5)Ni_(0.5)W₁O_(z′″). E is at least one cation selected from thegroup consisting of cations of: Fe, Ca, Mn, Sr, Eu, La, Zr, Ga, Sn andPb. E is preferably Fe, Sr, Zr, Ga or Pb, and preferred compounds offormula V are V₁Mo_(2.3)Ni_(0.5)Co_(0.5)Fe₁O_(z″″),V₁Mo_(2.3)Co_(0.5)Ni_(0.5)Sr₁O_(z″″),V₁Mo_(2.3)Co_(0.5)Ni_(0.5)Zr₁O_(z″″),V₁Mo_(2.3)Co_(0.5)Ni_(0.5)Ga₁O_(z″″) andV₁Mo_(2.3)Co_(0.5)Ni_(0.5)Pb₁O_(z″″).

[0047] The ranges for z, z′, z″, z′″, and z″″ defining the subscript foroxygen in the formulae I-V, varies widely. The value of z, z′, z″, z′″,and z″″ is defined using the range of possible oxidation states of allof the cations found in the molybdenum compound as shown below.

[0048] For the molybdenum compounds of formula I, the highest oxidationstates of the A cations are: V⁵⁺, Mo⁶⁺, Cr⁶⁺, Sb⁵⁺, Co³⁺, Ce⁴⁺ and Pb⁴⁺;and the lowest oxidation states for the A cations are: V³⁺, Mo⁴⁺, Cr²⁺,Sb³⁺, Co²⁺, Ce³⁺ and Pb²⁺. Therefore, for example, when the molybdenumcompound of formula I is V₁₀Mo₁A₁₀)_(z), wherein A is Cr, the maximumvalue for z. z_(max), is: z_(max)=((10×5)+(1×6)+(10×6))÷by 2=116/2=58.The minimum value for z, z_(min), in formula I wherein A is Cr is:z_(min)=((10×3)+(1×4)+(10×2))÷by 2=54/2=27. When the molybdenum compoundof formula I is V_(0.1)Mo₁A_(0.1)O_(z), wherein A is Pb,z_(max)=((0.1×5)+(1×6)+(0.1×4))÷by 2=6.9/2=3.45. The minimum value forz, z_(min), in formula I wherein A is Pb is:z_(min)=((0.1×3)+(1×4)+(0.1×2))÷by 2=4.5/2=2.25. Thus, for molybdenumcompounds of formula I, z ranges from 2.25 to 58.

[0049] For molybdenum compounds of formula II, the highest oxidationstates are: Ni³⁺, Mo⁶⁺, Sb⁵⁺, Al³⁺, and W⁶⁺ and the lowest oxidationstates are: Ni²⁺, Mo²⁺, Sb³⁺, Al³⁺, and W²⁺. z′_(max) and z′_(min) canbe calculated as shown above for z_(max) and z_(min) of formula I.

[0050] For molybdenum compounds of formula III, the highest oxidationstates are, V⁵⁺, Ni³⁺, Mo⁶⁺, Fe³⁺, Zn²⁺, Al³⁺, Sb⁵⁺, Bi⁵⁺, W⁶⁺, Li¹⁺,Ba²⁺, Nb⁵⁺, and Sn⁴⁺, and the lowest oxidation states are: V²⁺, Ni²⁺,Mo²⁺, Fe²⁺, Zn²⁺, Al³⁺, Sb³⁺, Bi³⁺, W²⁺, Li¹⁺, Ba²⁺, Nb³⁺, and Sn²⁺.z″_(max) and z″_(min) can be calculated as shown above for z_(max) andz_(min) of formula I. Since there can be mixtures of the C cations,these must be factored into the ranges for z.

[0051] For molybdenum compounds of formula IV, the highest oxidationstates are: Co³⁺, Ni³⁺, Mo⁶⁺, Ba²⁺, Mn⁷⁺, Al³⁺, Sb⁵⁺, Sn⁴⁺, and W⁶⁺, andthe lowest oxidation states are: Co²⁺, Ni¹⁺, Mo²⁺, Ba²⁺, Mn²⁺, Al³⁺,Sb³⁺, Sn²⁺, and W²⁺. z′″_(max) and z′″_(min) can be calculated as shownabove for z_(max) and z_(min) of formula I.

[0052] For molydbenum compounds of formula V, the highest oxidationstates are: V⁵⁺, Ni³⁺, Co³⁺, Mo⁶⁺, Fe³⁺, Ca²⁺, Mn⁷⁺, Sr²⁺, Eu³⁺, La³⁺,Zr^(4′), Ga³⁺, Sn⁴⁺ and Pb⁴⁺, and the lowest oxidation states are: V²⁺,Ni²⁺, Co²⁺, Mo²⁺, Fe²⁺, Ca²⁺, Mn²⁺, Sr²⁺, Eu²⁺, La³⁺, Zr⁴⁺, Ga³⁺, Sn²⁺and Pb²⁺. z″″_(max) and z″″_(min) can be calculated as shown above forz_(max) and z_(min) of formula I.

[0053] The catalysts of the present invention can be either a particularstructure (containing a certain ratio of cations) or a combination ofstructures and thus comprise a mixture of the crystalline oxides of themolybdenum compound of formula I, II, III, IV or V and may furthercomprise the amorphous phase of the compound.

[0054] The molybdenum compounds of the present invention can be preparedby various methods, for example, by freeze drying. alcohol reflux andgel techniques. Spray roasting, spray drying and coprecipitation couldalso be employed. Ceramic methods, i.e., solid state techniques could beused but are, in general, less preferred. Certain compounds of formulasI-V are better prepared by one method over another as appreciated by oneof ordinary skill in the art.

[0055] The catalyst preparative process is usually conducted at normalatmospheric pressure, but elevated or reduced pressures can be employed.Agitation is not required, but is usually provided to facilitate ahomogeneous mix and to facilitate heat transfer.

[0056] One process for the preparation of a catalyst comprising amolybdenum compound of formulas I, II, III, IV, V, VI or VII, asdescribed above, comprises contacting at least one cation containingcompound with at least one cation containing compound for each of theother cations of the final molybdenum compound in a solution comprisingwater to form a resultant solution or colloid; freezing the resultantsolution or colloid to form a frozen material; freeze drying the frozenmaterial; and heating the dried frozen material to yield the molybdenumcompound of formula I, II, III, IV, V, VI or VII.

[0057] The compound containing a cation of the final molybdenum compoundof formula I, II, III, IV, V, VI or VII can be a salt, oxide or thelike. The cation containing compounds are contacted with each other upontheir addition to the solution comprising water. There is at least onecation containing compound for each of the cations in the molybdenumcompound of formula I, II, III, IV, V, VI or VII. Each cation can becontained in a separate cation containing compound or more than onecation can be contained in the same cation containing compound. Therecan also be more than one cation containing compound for each cation inthe final molybdenum compound of formulas I, II, III, IV. V, VI or VII.The cation containing compounds can be ammonium or sodium salts ofmolybdic acid, vanadic acid or tungstic acid, in addition to compoundscontaining the A, B, C, D, E cation of choice or other cations presentin the final molybdenum compound of formulas I, II, III, IV, V, VI orVII. For example, the oxides or acetylacetonates, chlorides or acetatesof Li, Cr, Mn, Mo. Fe, Co, Ni, Ce, W, Zn, Sr, Nb, Eu, Ba, Zr, Al, Ca,Sn, Pb, Sb, Bi, La and Ga can be cation containing compounds.Representative examples of such salts or oxides containing cations ofthe final molybdenum compound of formula I, II, III, IV, V, VI or VIIcan be found in Tables 1-6 of the present invention. Normal commerciallyavailable reagents can be used for the cation containing compounds usedin the preparation of the molybdenum compound. The highest purityproducts attainable need not be employed, however the purity of thereagents must be known in order to calculate the gross amount required.In addition the reagents should not be contaminated with any catalystpoison. The amount of reagent employed should be within plus or minus5%, preferably within plus or minus 2% of the amount indicated bystoichiometry.

[0058] The cation containing compounds are dissolved in an appropriatesolvent to form a solution or fine colloid. The formation of a solution,as opposed to a colloid, is generally preferred for most effectivemixing.

[0059] In cases where NH₄VO₃ is the cation containing compound used,NH₄VO₃ salt can be dissolved in water prior to adding the other cationcontaining compounds by heating water or other appropriate solvents. Theadditional cation containing compounds can then be added to form aresultant solution or a finely mixed colloid. The resultant solution orcolloid is rapidly frozen at liquid nitrogen temperatures. Rapidfreezing ensures the cation containing compounds will remain intimatelymixed and will not segregate to any significant degree. The frozenmaterial can then be transferred to a freeze drier, such as a VirtisFreeze Drier (Baltimore, Maryland) equipped with a Unitop unit. Thesolution is kept frozen while water vapor is removed by evacuation. Inorder to prevent melting of the frozen material, the freeze drier can bemaintained at a temperature ranging from about 0° C. to about 40° C.,preferably between −40° C. to −20° C. with a vacuum of 2-10 millitorr.After at least 24 hours, preferably about 2-4 days, the dried sample canbe calcined (heated) in air at a temperature ranging from about 250° C.to about 500° C., preferably about 400° C., for a time sufficient todecompose the cation containing compounds of formula I, II, III, IV, V,VI or VII to form metal oxide phases. This will require heating for aperiod of about 0.5 hours to about 24 hours.

[0060] Freeze drying methods can produce mixtures of solid cationcontaining compounds which are nearly as well mixed as their solutioncounterparts. The method is superior to slower solvent evaporationbecause homogeneity can be lost during the removal of solvent. Inaddition, in many cases because the cation containing compounds are wellmixed, a lower calcination temperature can be used, and can allow forthe synthesis of metal oxides with higher surface areas than typicallyobserved by traditional high temperature ceramic syntheses. Choice ofcalcination temperature and protocols and atmosphere can also influencethe types of phases synthesized.

[0061] Another process for the preparation of a catalyst comprising amolybdenum compound of formula I, II, III, IV, V, VI or VII, asdescribed above, comprises the steps of: mixing a solution comprising atleast one cation containing compound for each of the cations in themolybdenum compound of formula I, II, III, IV, V, VI, VI or VII and analcohol to form a suspension; heating the suspension to reflux; andisolating the molybdenum compound of formula I, II, III, IV, V, VI orVII.

[0062] At least one cation containing compound for each of the cationsin the molybdenum compound of formula I, II, III, IV, V, VI or VII arecombined with an alcohol or combination of alcohols, such as ethylalcohol, ethyl alcohol/benzyl alcohol mixtures, 1-propanol, 1-butanol,isobutyl alcohol, 2-methyl-2 propanol, 1-heptanol, neopentyl alcohol,phenol or the like, to form a suspension. The cation containingcompounds can be those as described above for the freeze drying process.Mixing or agitation can be supplied via methods known in the art. Thepreparation can be carried out in a dry box to prevent any hydration.The resulting suspension is next heated to reflux under an inertatmosphere, such as nitrogen, for a time sufficient to ensure a propersolution. After the solution is formed, the solvent can be removed byfreeze drying, rotary-evaporation, or a slow drying process afterfiltering, decanting or the like. The dried material can then becalcined at a temperature ranging from about 250° C. to about 500° C.,preferably about 400° C., under air for a time sufficient to form themolybdenum compound of formula I, II, III, IV, V, VI or VII. This cantake from about 0.5 hours to about 24 hours.

[0063] A further process for the preparation of a catalyst comprising amolybdenum compound of formula I, II, III, IV, V, VI or VII, asdescribed above, comprises the steps of: contacting at least one cationcontaining compound for each cation of the molybdenum compound offormula I, II, III, IV, V, VI or VII with at least one cation containingcompound for each of the other cations in the molybdenum compound offormula I, II, III, IV, V, VI or VII in a solution comprising water toform a resultant solution or colloid; stirring the resultant solution orcolloid until gelation occurs; and drying the gel to yield themolybdenum compound of formula I, II, III, IV, V, VI or VII.

[0064] The cation containing compounds for this gel process can be thoseas described above for the freeze drying process. Following contact ofthe cation containing compounds with each other, the resultant solutionor colloid is stirred until gelation occurs. In some cases an adjustmentof pH is needed to induce gelation. Acid or base can be added dependingon the nature of the other ingredients being used in the preparation ofthe molybdenum compound. Gelation can occur at room temperature atatmospheric pressure. The resulting gel can be dried and then calcinedat a temperature ranging from about 250° C. to about 450° C., preferably400° C., under air for a time sufficient to thoroughly dry.

[0065] Compounds of formula I, II, III, and V of the present inventionare useful as catalysts in the oxidation of C4 hydrocarbons. The presentinvention provides a process for the oxidation of C4 hydrocarbons tomaleic anhydride, comprising: contacting the C4 hydrocarbon with asource of oxygen in the presence of a catalytic amount of a catalystcomprising a molybdenum compound of formula I, II, III or V as definedabove. The C4 hydrocarbon is selected from the group consisting of:n-butane, 1-butene, 2-butene and butadiene, and isomers thereof.

[0066] In some instances the catalyst may be useful as a lattice oxygencatalyst in the oxidation of C4 hydrocarbons with the ability toselectively oxidize the C4 hydrocarbon in the absence of gas phaseoxygen and thus can be the only source of oxygen.

[0067] The catalyst comprising the molybdenum compound of formula I, II,III or V can be used alone, supported on a catalyst support orimpregnated in a carrier material. Typical support carrier materials arewell known to those skilled in the art as are methods of preparingsupported or impregnated catalysts. Typical materials comprise silica,titania, zirconia, alumina, thoria, silicon carbide and carbon. Thecatalyst comprising the molybdenum compound described herein can be usedas isolated, or in cases where size and shape of the catalyst isdictated by the requirements of the equipment employed in the subsequentuse of the catalyst, the catalyst can be processed or fabricated intovarious size and shape particles before use by grounding, pelletizing,briquetting, tabulating, or shaping in other ways as required.

[0068] A first group of compounds, listed in Table 1 as Examples 1-5,are of formula I: V_(q)MoA_(y)O_(z), where q varies from 0.1 to 10, yvaries from 0.1 to 10, A is at least one cation selected from the groupconsisting of cations of Cr, Sb, Co, Ce and Pb, and z is calculated asabove. The performance of these molybdenum compounds as catalysts in theoxidation of n-butane is shown in Table 1.

[0069] A second group of compounds, listed in Table 1 as Examples 6-9,are of formula II: NiMo_(x)B_(y)O_(z′), where x varies from 0.1 to 10, yvaries from 0.1 to 10, B is at least one cation selected from the groupconsisting of cations of Sb, Al and W and z′ is calculated as above. Theperformance of these molybdenum compounds as catalysts in the oxidationof n-butane is shown in Table 2.

[0070] A third group of compounds, listed in Table 3 as Examples 10-21,are of formula III: VNi_(w)Mo_(x)C_(y′)O_(z″), where w varies from 0.1to 10, x varies from 0.1 to 10, y′ varies from 0 to 10, C is at leastone cation selected from the group consisting of cations of Fe, Zn, Al,Sb. Bi, W, Li, Ba, Nb and Sn and z″ is calculated as above. Theperformance of these molybdenum compounds as catalysts in the oxidationof n-butane is shown in Table 3.

[0071] Another group of compounds, listed in Table 5 as Examples 27-35,are of formula V: VNi_(w)Co_(r)Mo_(x)E_(y)O_(z″″), where w varies from0.1 to 10, r varies from 0.1 to 10, x varies from 0.1 to 10, y variesfrom 0.1 to 10, E is at least one cation selected from the groupconsisting of cations of Fe, Ca, Mn, Sr, Eu, La, Zr, Ga, Sn and Pb andz″″ is calculated as above. The performance of these molybdenumcompounds as catalysts in the oxidation of n-butane is shown in Table 5.

[0072] The present invention further provides a process for theoxidation of n-butane to maleic anhydride comprising contacting n-butanewith a source of oxygen in the presence of a catalytic amount of acatalyst comprising a molybdenum compound of formula IV, as definedabove, in a bulk state. In some instances the catalysts comprising amolybdenum compound of formula IV of the present invention are used ascatalysts in the bulk state, i.e., not on a support, but as purecompounds. The catalyst comprising the molybdenum compound of formula IVmay be the only source of oxygen. The catalytic oxidation can be carriedout in a fixed or fluidized bed reactor.

[0073] A group of compounds, listed in Table 4 as Examples 22-26, are offormula IV: CoNi_(w)Mo_(x)D_(y)O_(z′″), where w varies from 0.1 to 10, xvaries from 0.1 to 10, y varies from 0.1 to 10, D is at least one cationselected from the group consisting of cations of Ba, Mn, Al, Sb, Sn andW, and z′″ is calculated as above. The performance of these molybdenumcompounds as catalysts in the oxidation of n-butane is shown in Table 4.

[0074] The present invention also provides a process for the oxidationof n-butane to maleic anhydride, comprising: contacting n-butane with asource of oxygen in the presence of a catalytic amount of a catalystcomprising a molybdenum compound of formula VI or VII in a crystalline,active phase

[0075] VI V₉Mo₆O₄₀

[0076] VII V₂MoO₈

[0077] to yield maleic anhydride. Prepared as herein described, themolybdenum compound of formula VI or VII is formed with little MoO₃by-product. The performance of this molybdenum compound in acrystalline, active phase as a catalyst in oxidation of n-butane isshown in Example 36 of Table 6.

[0078] Comparative Examples 37-41, not of this invention, and theperformance of these materials as catalysts in the oxidation of n-butaneis listed in Table 7.

[0079] Prior to use in the microreactor, the catalysts described hereinare typically formed into a convenient catalyst shape by pelletizing thecatalyst at about 30,000 psi (2.07×10⁶ kPa) or less, to form small disksand crushing the pellet through sieves. For fixed bed reactorevaluations, typically a −40, +60 mesh is used (U.S. Sieve Series).Optionally, one could blend the resultant powder with 1-3% of a dielubricant and pellet binder, such as graphite or Sterotex®, ahydrogenated cottonseed oil, commercially available from Capital CityProducts Company, Columbus. Ohio, before tabletting. For fluidized bedreactor use, the preferred size range is 20 to 150 micrometers.

[0080] Glass and stainless steel are usually employed as the material ofconstruction for the microreactor. This is not critical as long asmaterials that contaminate the product with catalyst poisons are notemployed.

[0081] Although processes of the invention are embodied in the followinglaboratory scale examples, Applicant notes that the invention can bepracticed on an industrial scale by making the necessary engineering anddesign modifications which are customary in the art.

[0082] Catalytic oxidation using a catalyst comprising a molybdenumcompound of formula I, II, III, IV, V, VI or VII can be carried out in afixed or fluidized bed reactor or recirculating solids reactor. Thesecatalysts can be utilized advantageously with regard to conversion andselectivity in the wide variety of conventional techniques and reactorconfigurations employed to conduct the vapor phase oxidation of C4hydrocarbons to maleic anhydride. For example, the conversion can beconducted in a fixed-bed reactor, whereby the catalyst particles aremaintained in a fixed position and are contacted with C4 hydrocarbon anda source of oxygen, typically molecular oxygen, both in appropriateamounts, optionally in the presence of one or more inert diluent gases,at a temperature varying between 200° C. and about 450° C., preferablybetween about 300° C. and about 350° C. The greatest advantages of usingthe catalyst of this invention are realized when the conversion of C4hydrocarbon to maleic anhydride is carried out in a recirculating solidsreactor, such as that described in U.S. Pat. No. 4,668,802. This patentdiscloses an improved process for the selective vapor phase oxidation ofn-butane to maleic anhydride over a vanadium/phosphorus/oxygen (VPO)catalyst, whereby the amount of oxygen in the feed gas to the VPOcatalyst is limited to less than the stoichiometric amount required forthe total amount of n-butane converted in the process. The reducedcatalyst resulting from the oxidation is separated from the gaseousproduct stream and is reoxidized, optionally in a separate reactionzone, before being contacted with n-butane.

[0083] The catalysts of the present invention demonstrate good resultsin activity, conversion and selectivity. Tables 1-6 below showconversion and selectivity after 1 sec and after 3 sec for variouscatalysts of the present invention and compare these results with thoseof other catalysts in the art (Table 7).

EXAMPLES

[0084] The reagents for the following examples are commerciallyavailable as follows: NH₄VO₃, Cr₂O₃, (CH₃CO₂)₇Cr₃(OH)₂, Ce(SO₄)₂,Fe(NO₃)₃-9H₂O, NbCl₅, Co(NO₃)₂-6H₂O, (CH₃CO₂)₂Mn-4H₂O, V₂O₅ andLa(NO₃)₃-5H₂O from Aldrich, Milwaukee, Wis.; NH₄VO₃, MoO₃,Ni(OOCCH₃)₂-4H₂O, NiCl₂-6H₂O, H₂WO4, LiNO₃ (anhydrous), SnCl₂,(NH₄)₁₀W₁₂O₄₁-5H₂O, Co(NO₃)₂-6H₂O, and SnCl₂ from Alfa, Ward Hill,Mass., (NH₄)₆Mo₇O₂₄-4H₂O), Ni(NO₃)-6H₂O, Al(NO₃)₃-9H₂O, Bi(NO₃)₃-5H₂O,Ni(NO₃)₂-6H₂O, Co(NO₃)₂-6H₂O, Al(NO₃)₃-9H₂O, Ca(NO₃)₂-4H₂O, andNi(NO₃)₂, from Baker, Phillipsburg, N.J.; Pb(NO₃)₂, NiCl₂-6H₂O,Pb(NO₃)₂, and H₃PO₄ from EM Sciences, Gibbstown, N.J.;(NH₄)₆Mo₇O₂₄-4H₂O) from Mallinchkrodt, Erie, Pa.; NH₄VO₃, Sb(OOCCH₃)₃,Co(OOCCH₃)₂, Zr(SO₄)₂-4H₂O and Ga(NO₃)₃ from J&M, Ward Hill, Mass.;colloidal (Al₂O₃) from Nyacol, Ashland, Mass.; Zn(NO₃)₂-6H₂O fromFisher, Fairlane, N.J.; and Ba(NO₃)₂ and EuCl₂ from AESAR, Ward Hill,Mass.

General Procedure for Freeze Drying

[0085] The component salts (indicated in the tables) were added to theindicated amount of water. In cases where NH₄VO₃ was used, the salt wasdissolved in water prior to adding the other components by bringing thesolvent to a boil. The additional salts were then added to form thesolution or finely mixed colloid/slurry. The resultantsolutions/colloids were rapidly frozen in glass dishes (3″ diameter)using liquid nitrogen. The frozen material was then transferred to aVirtis Freeze Drier (Baltimore, Md.) equipped with a Unitop unit. Inorder to prevent melting of the frozen solid, the Unitop chamber shelveswere maintained between 40 to −20° C. with a vacuum of 2-10 millitorr.After at least 24 hours (usually 24 days), the dried sample was calcined(heated) in air to 400° C. for 5 hours to produce the final catalystproduct. Prior to microreactor evaluations, the material was pelletizedat 20,000 psi and crumbled and screened on −40, +60 mesh screens.

General Procedure for Alcohol Reflux Specific Preparation of V₂MoO₈

[0086] Vanadium pentoxide. V₂O₅, 90.94 g 0.500 mol, and molybdic oxide.MoO₃, 71.97 g, 0.500 mol were combined in an round bottomed flaskequipped with an agitator with 1034 ml of isobutyl alcohol and 95 ml ofbenzyl. The resulting suspension was heated to reflux under a nitrogenatmosphere for 16 hours. The resulting green suspension was filtered andthe isolated product dried and then calcined at 400° C. under air for 5hours.

General Procedure for Gel Method Specific Preparation ofNiMo_(2.3)AlO_(′)

[0087] 35 ml of water was added to the colloidal alumina (20% byweight). The solid oxide and nickel acetate was added. The mixture wasstirred until gelation occurred. The gel was dried then calcined at 400°C. under air for 5 hours.

Micro-Reactor Evaluation of Butane Oxidation Catalysts

[0088] The catalysts were pelletized at 1.38×10⁶ kPa into disks andsubsequently crushed and sieved through (−40, +60) mesh screens.Approximately 0.9 cc of catalyst were used for each evaluation.

[0089] The catalyst testing facility consisted of six micro-reactorswhich were connected to a common feed source and a common analytical gaschromatograph (GC). Each of the micro-reactors consisted of a 5.0 cm by0.64 cm stainless steel tube which was immersed in an individualsandbath to maintain isothermal conditions. The feed composition andindividual reactor flow rates were metered by commercially availablemass flow controllers (Tylan Model FC-260, available from Tylan Corp.,Torrance, Calif.). All exit gas lines were heated to 200° C. andconnected to a multiport Valco valve for the on-line analysis ofproducts using a commercially available GC (Hewlitt-Packard 5890 SeriesII, Hewlitt-Packard, Palo Alto, Calif.). A computer program controlledthe Valco valve to select a reactor or feed stream to fill the 0.5 mlsample loop for injection in the GC. The GC was used to analyze forbutane, maleic anhydride, acetic acid, acrylic acid, other C₁ to C₄hydrocarbons, oxygen. carbon monoxide, carbon dioxide, nitrogen andwater.

[0090] The standard testing protocol for butane oxidation catalysts wasdeveloped to measure maleic anhydride selectivities and yields underhydrocarbon-lean conditions (2% n-butane, 20% oxygen) over a range ofbutane conversions. Temperature was varied from 350° to 380° to 400° andback to 350° C., with three contact times (nominally 3, 1, and 0.5 s)evaluated at each temperature. The temperature was returned to 350° C.to provide information about the equilibration of the catalyst. Theconversion and selectivity of two representative evaluations (at 380°C.) are reported in the tables below. TABLE 1 380° C., 2.0% Butane/Air 1sec 3 sec Composition Gram Mole Method of Conversion SelectivityConversion Selectivity V_(q)MoA_(y)O_(z) Example Salt Used WeightSolvent Synthesis % % % % V₁Mo₁Cr₁O_(z) 1 NH₄VO₃, 50% 116.98 250 ml H₂Ofreeze-dried 41 6 75 2 V₂O₅ 50% 181.90 Cr₂O₃ 151.99 (CH₃CO₂)₇Cr₃(OH)₂602.32 (NH₄)₆Mo₇O₂₄—4H₂O 1235.90 MoO₃ 143.94 V₁Mo₁Sb₁O_(z) 2 NH₄VO₃116.98 250 ml H₂O freeze-dried 75 7 99 2 (NH₄)₆Mo₇O₂₄—4H₂O 1235.90Sb(OOCCH₃)₃ 298.88 V₁Mo₁Co₁O_(z) 3 NH₄VO₃ 116.98 250 ml H₂O freeze-dried70 3 99 0 (NH₄)₆Mo₇O₂₄—4H₂O 1235.90 Co(OOCCH₃)₂ 177.023 V₁Mo₁Ce₁O_(z) 4NH₄VO₃ 116.965 250 ml H₂O freeze-dried 18 9 45 4 (NH₄)₆Mo₇O₂₄—4H₂O1235.9 Ce(SO₄)₂ 332.24 V₁Mo₁Pb₁O_(z) 5 NH₄VO₃ 116.965 250 ml H₂Ofreeze-dried 15 8 33 4 (NH₄)₆Mo₇O₂₄—4H₂O 1235.9 Pb(NO₃)₂ 331.2

[0091] TABLE 2 380° C., 2.0% Butane/Air 1 sec 3 sec Composition GramMole Method of Conversion Selectivity Conversion SelectivityNiMo_(x)B_(y)O_(z′) Example Salt Used Weight Solvent Synthesis % % % %Ni₁Mo_(2.3)Sb₁O_(z′) 6 Sb(OOCCH₃)₃ 298.88 59 cc of freeze-dried 10 21 2612 (NH₄)₆Mo₇O₂₄—4H₂O 1235.9 30% HCl Ni(OOCCH₃)₂—4H₂O 248.82Ni₁Mo_(2.3)Al₁O_(z′) 7 Ni(OOCCH₃)₂—4H₂O 248.8212 35 ml H₂O gel 21  6 46<1 (NH₄)₆Mo₇O₂₄—4H₂O 1235.9 colloidal (Al₂O₃) 20% 101.9613 by wt.Ni₁Mo_(1.3)W₁O_(z′) 8 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 50 ml H₂O freeze-dried10 13 24 2 NiCl₂—6H₂O 237.71 70 ml NH₄OH H₂WO₄ 249.86Ni₁Mo₁W_(1.3)O_(z′) 9 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 40 ml H₂O freeze-dried10 11 35 0 NiCl₂—6H₂O 237.71 90 ml NH₄OH H₂WO₄ 249.86 25 ml H₂O

[0092] TABLE 3 380° C., 2.0% Butane/Air Gram 1 sec 3 sec CompositionExam- Mole Method of Conversion Selectivity Conversion SelectivityVNi_(w)Mo_(x)C_(y′)O_(z″) ple Salt Used Weight Solvent Synthesis % % % %V₁Mo_(2.3)Ni₁O_(z″) 10 NH₄VO₃ 116.98 100 cc H₂O freeze- 40 21 71 15(NH₄)₆Mo₇O₂₄—4H₂O 1235.86 100 cc H₂O dried NiCl₂—6H₂O 237.71 20 cc HClV₁Mo_(2.3)Ni₁Fe₁O_(z″) 11 NH₄VO₃ 116.98 100 cc H₂O freeze- 28 7 60 <1(NH₄)₆Mo₇O₂₄—4H₂O 1235.86 100 cc H₂O dried Ni(NO₃)—6H₂O 290.81 20 ccHNO₃ Fe(NO₃)₃—9H₂O 404 V₁Mo_(2.3)Ni₁Zn₁O_(z″) 12 NH₄VO₃ 116.98 100 ccH₂O freeze- 53 6 83 <1 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 100 cc H₂O driedNi(NO₃)—6H₂O 290.81 20 cc HNO₃ Zn(NO₃)₂—6H₂O 297.47V₁Mo_(2.3)Ni₁Al₁O_(z″) 13 NH₄VO₃ 116.98 100 cc H₂O freeze- 45 5 79 0(NH₄)₆Mo₇O₂₄—4H₂O 1235.86 100 cc H₂O dried Ni(NO₃)—6H₂O 290.81 20 ccHNO₃ Al(NO₃)₃—9H₂O 375.13 V₁Mo_(2.3)Ni₁Sb₁O_(z″) 14 NH₄VO₃ 116.98 100 ccH₂O freeze- 39 10 69 5 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 100 cc H₂O driedNi(NO₃)—6H₂O 290.81 15 cc HNO₃ Sb(OOCCH₃)₃ 298.88 50 cc HClV₁Mo_(2.3)Ni₁Bi₁O_(z″) 15 NH₄VO₃ 116.98 100 cc H₂O freeze- 20 15 50 7(NH₄)₆Mo₇O₂₄—H₂O 1235.86 100 cc H₂O dried Ni(NO₃)—6H₂O 290.81 20 cc HNO₃Bi(NO₃)₃—5H₂O 485.07 30 cc HNO₃ V₁Mo_(2.3)Ni₁W₁O_(z″) 16 NH₄VO₃ 116.98100 cc H₂O freeze- 30 10 71 2 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 100 cc H₂O driedNi(NO₃)—6H₂O 290.81 20 cc HNO₃ H₂WO₄ 249.86 V₁Mo_(2.3)Ni₁Li₁O_(z″) 17NH₄VO₃ 116.98 100 ml H₂O freeze- 11 17 20 11 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86dried NiCl₂—6H₂O 237.71 15 ml HCl LiNO₃ (anhydrous) 68.9459V₁Mo_(2.3)Ni₁Ba₁O_(z″) 18 NH₄VO₃ 116.98 100 ml H₂O freeze- 35 10 66 2(NH₄)₆Mo₇O₂₄—4H₂O 1235.86 100 ml H₂O dried Ni(NO₃)—6H₂O 290.81 20 mlHNO₃ Ba(NO₃)₂ 261.3398 V₁Mo_(2.3)Ni₁Nb₁Fe₁O_(z″) 19 NH₄VO₃ 116.98 100 ccH₂O freeze- 30 3 60 <1 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86  50 cc H₂O driedNiCl₂—6H₂O 237.71 20 cc HCl NbCl₅ 270.71 70 cc HCl Fe(NO₃)₃—9H₂O 404V₁Mo_(2.3)Ni₁Nb₁Sn₁O_(z″) 20 NH₄VO₃ 116.98 100 ml H₂O freeze- 40 12 68 3(NH₄)₆Mo₇O₂₄—4H₂O 1235.86  70 ml H₂O dried NiCl₂—6H₂O 237.71 20 ml HClNbCl₅ 270.17 20 ml HCl SnCl₂ 189.61  50 ml H₂O V₁Mo_(2.3)Ni₁W₁Sn₁O_(z″)21 (NH₄)₁₀W₁₂O₄₁— 3132.64 140 ml freeze- 25 10 47 3 5H₂O 1235.86 NH₄OHdried (NH₄)_(5Mo) ₇O₂₄—4H₂O 116.98 NH₄VO₃ 290.81  50 ml H₂ONi(NO₃)₂—5H₂O 189.61 SnCl₂  5 ml HCl

[0093] TABLE 4 380° C., 2.0% Butane/Air 1 sec 3 sec Composition Exam-Gram Mole Method of Conversion Selectivity Conversion SelectivityCoNi_(w)Mo_(x)D_(y)O_(z″) ple Salt Used Weight Solvent Synthesis % % % %Co_(0.5)Ni_(0.5)Mo₃ 22 Co(NO₃)₂—6H₂O 291.03  20 ml H₂O freeze-dried 12.532 29 27 Sn_(0.5)O_(z′′′) SnCl₂ 189.61 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86  50 mlH₂O NiCl₂—6H₂O 237.71 20 ml HNO₃ Mo₃Co_(0.5)Ni_(0.5) 23 Co(NO₃)₂—H₂O291.03  20 ml H₂O freeze-dried 1.3 4 2.3 11 Mn₁O_(z′′′) (CH₃CO₂)₂Mn—4H₂O245.09 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86  30 ml H₂O NiCl₂—6H₂O 237.71  20 ml H₂OMo₃Co_(0.5)Ni_(0.5) 24 Co(NO₃)₂—6H₂O 291.03  20 ml H₂O freeze-dried 0.816 2.1 18 Ba₁O_(z′′′) Ba(NO₃)₂ 261.34 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86  80 mlH₂O NiCl₂—6H₂O 237.71  20 ml H₂O Mo₃Co_(0.5)Ni_(0.5) 25 Co(NO₃)₂—6H₂O291.03  20 ml H₂O freeze-dried 3.9 15 10.5 8 Al₁O_(z′′′) Al(NO₃)₃—9H₂O375.13 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 150 ml H₂O NiCl₂—6H₂O 237.71  20 ml H₂OMo₃Co_(0.5)Ni_(0.5) 26 Co(NO₃)₂—6H₂O 291.03  40 ml H₂O freeze-dried 4.227 14.2 15 W₁O_(z′′′) (NH₄)₁₀W₁₂O₄₁—5H₂O 3132.64 (NH₄)₆Mo₇O₂₄—4H₂O1235.86  50 ml H₂O NiCl₂—6H₂O 237.71  10 ml H₂O

[0094] TABLE 5 380° C., 2.0% Butane/Air Gram 1 sec 3 sec CompositionMole Method of Conversion Selectivity Conversion SelectivityVNi_(w)Co_(r)Mo_(x)E_(y)O_(z′′′) Example Salt Used Weight SolventSynthesis % % % % V₁Mo_(2.3)Ni_(0.5)Co_(0.5) 27 NH₄VO₃ 116.98 50 ml H₂Ofreeze-dried 15 13 32 7 Fe₁O_(z″″) (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 20 ml H₂OCo(OOCCH₃)₂ 177.02 20 ml HCl Ni(NO₃)₂—6H₂O 290.81 Fe(NO₃)₃—9H₂O 404 20ml H₂O V₁Mo_(2.3)Ni_(0.5)Co_(0.5) 28 NH₄VO₃ 116.98 50 ml H₂Ofreeze-dried 14 10 34 4 Ca₁O_(z″″) (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 Co(OOCCH₃)₂177.02 20 ml HCl Ni(NO₃)₂—6H₂O 290.81  5 ml HCl Ca(NO₃)₂—4H₂O 236.15V₁Mo_(2.3)Co_(0.5)Ni_(0.5) 29 NH₄VO₃ 116.98 50 ml H₂O freeze-dried 12.52.5 29.2 1 Mn₁O_(z″″) (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 20 ml H₂O Co(OOCCH₃)₂177.02 20 ml HCl Ni(NO₃)₂—6H₂O 290.81 (CH₃CO₂)₂Mn—4H₂O 245.09 10 ml H₂OV₁Mo_(2.3)Co_(0.5)Ni_(0.5) 30 NH₄VO₃ 116.98 50 ml H₂O freeze-dried 21 1747 10 Sr₁O_(z″″) (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 20 ml HCl Co(OOCCH₃)₂ 177.0210 ml H₂O Ni(NO₃)₂—6H₂O 290.81 Sr(NO₃)₂ 211.63V₁Mo_(2.3)Co_(0.5)Ni_(0.5) 31 NH₄VO₃ 116.98 50 ml H₂O freeze-dried 247.5 54 2 Eu₁O_(z″″) (NH₄)₆Mo₇O_(24—4H) ₂O 1235.86 Co(OOCCH₃)₂ 177.02 20ml HCl Ni(NO₃)₂—6H₂O 290.81 EuCl₂ 222.87 10 ml H₂OV₁Mo_(2.3)Co_(0.5)Ni_(0.5) 32 NH₄VO₃ 116.98 50 ml H₂O freeze-dried 17 1036 5 La₁O_(z″″) (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 Co(OOCCH₃)₂ 177.02 20 ml HClNi(NO₃)₂—6H₂O 290.81 La(NO₃)₃—5H₂O 415.01 10 ml H₂OV₁Mo_(2.3)Co_(0.5)Ni_(0.5) 33 NH₄VO₃ 116.98 50 ml H₂O freeze-dried 2017.5 46 12 Zr₁O_(z″″) (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 Co(OOCCH₃)₂ 177.02 20 mlHCl Ni(NO₃)₂—6H₂O 290.81 Zr(SO₄)₂—4H₂O 355.32 40 ml H₂OV₁Mo_(2.3)Co_(0.5)Ni_(0.5) 34 NH₄VO₃ 116.98 50 ml H₂O freeze-dried 1816.5 43 11 Ga₁O_(z″″) (NH₄)₆Mo₇O₂₄—4H₂O 1235.86 Co(OOCCH₃)₂ 177.02  20ml HCl Ni(NO₃)₂—6H₂O 290.81 Ga(NO₃)₃ 255.74 V₁Mo_(2.3)Co_(0.5)Ni_(0.5)35 NH₄VO₃ 116.98 50 ml H₂O freeze-dried 22 20 47 14 Pb₁O_(z″″)(NH₄)₆Mo₇O₂₄—4H₂O 1235.86 (with dry ice Co(OOCCH₃)₂ 177.02 20 ml HCl andacetone) Ni(NO₃)₂—6H₂O 290.81 Pb(NO₃)₂ 331.2 100 ml HCl 86 ml NH₄OH

[0095] TABLE 6 380° C., 2.0% Butane/Air Gram 1 sec 3 sec Mole Method ofConversion Selectivity Conversion Selectivity Composition Example SaltUsed Weight Solvent Synthesis % % % % V2Mo₁Ox 36 V₂O₅ 90.94 g 181.881034 ml isobutyl alcohol Alcohol reflux 60 10 90 0 MoO₃  71.97 g 143.9495 ml benzyl alcohol

[0096] TABLE 7 380° C., 2.0% Butane/Air 1 sec 3 sec Comp. Gram MoleMethod of Conversion Selectivity Conversion Selectivity CompositionExample Salt Used Weight Solvent Synthesis % % % % MoO₃ 37(NH₄)₆Mo₇O₂₄—4H₂O 1235.9 freeze-dried 11 <1 VPO 38 NH₄VO₃ 116.965freeze-dried 8 20 H₃PO₄ 97.97 Ni₁W_(2.3)O_(t) 39 H₂WO₄ 249.86  50 ml H₂Ofreeze-dried 2.5 0 9 0 NiCl₂—6H₂O 237.71 180 ml NH₄OH Ni₁Mo_(2.3)P₁O_(t)40 Ni(NO₃)₂ 290.8  50 ml H₂O freeze-dried 6 12 (NH₄)₆Mo₇O₂₄—4H₂O 1235.86100 ml H₂O H₃PO₄ 98 V₂O₅ 41 freeze-dried 80 <1

What is claimed is:
 1. A catalyst, comprising a molybdenum compound offormula I, II, III, IV or V: I V_(q)MoA_(y)O_(z) II NiMo_(x)B_(y)O_(z′)III VNi_(w)Mo_(x)C_(y′)O_(z′) IV CoNi_(w)Mo_(x)D_(y)O_(z′″) VVNi_(w)Co_(r)Mo_(x)E_(y)O_(z″″) wherein: q is a number from 0.1 to 10; ris a number from 0.1 to 10; w is a number from 0.1 to 10; x is a numberfrom 0.1 to 10; y is a number from 0.1 to 10; y is a number from 0 to10, A is at least one cation selected from the group consisting ofcations of: Cr, Sb, Co, Ce and Pb; B is at least one cation selectedfrom the group consisting of cations of: Sb, Al and W; C is at least onecation selected from the group consisting of cations of: Fe, Zn, Al, Sb,Bi, W, Li, Ba, Nb and Sn; D is at least one cation selected from thegroup consisting of cations of: Ba, Mn, Al, Sb, Sn, and W; E is at leastone cation selected from the group consisting of cations of: Fe, Ca, Mn,Sr, Eu, La, Zr, Ga, Sn and Pb: and z, z′, z″, z′″, and z″″ aredetermined using the amounts and oxidation states of all cations presentin each formula according to the following equations: z=((q timesoxidation state of V)+(1 times oxidation state of Mo)+(y times oxidationstate of A)) divided by 2 (oxidation state of oxygen); z′=((1 timesoxidation state of Ni)+(x times oxidation state of Mo)+(y timesoxidation state of B)) divided by 2 (oxidation state of oxygen); z″=((1times oxidation state of V)+(w times the oxidation state of Ni)+(x timesoxidation state of Mo)+(y′ times oxidation state of C)) divided by 2(oxidation state of oxygen); z=((1 times oxidation state of Co)+(w timesthe oxidation state of Ni)+(x times oxidation state of Mo)+(y′ timesoxidation state of D)) divided by 2 (oxidation state of oxygen); andz″″=((I times oxidation state of V)+(w times the oxidation state ofNi)+(r times the oxidation state of Co)+(x times oxidation state ofMo)+(y times oxidation state of E)) divided by 2 (oxidation state ofoxygen).
 2. The catalyst of claim I wherein the molybdenum compound isof formula I.
 3. The catalyst of claim 1 wherein the molybdenum compoundis of formula II.
 4. The catalyst of claim 1 wherein the molybdenumcompound is of formula III.
 5. The catalyst of claim I wherein themolybdenum compound is of formula IV.
 6. The catalyst of claim I whereinthe molybdenum compound is of formula V.
 7. A process for the oxidationof a C4 hydrocarbon to maleic anhydride, comprising: contacting a C4hydrocarbon with a source of oxygen in the presence of a catalyticamount of a catalyst comprising a molybdenum compound of formula I, II,III or V I V_(q)MoA_(y)O_(z) II NiMo_(x)B_(y)O_(z′) IIIVNi_(w)Mo_(x)C_(y′)O_(z″) V VNi_(w)Co_(r)Mo_(x)E_(y)O_(″″) wherein: q isa number from 0.1 to 10; r is a number from 0.1 to 10; w is a numberfrom 0.1 to 10; x is a number from 0.1 to 10; y is a number from 0.1 to10; y′ is a number from 0 to 10, A is at least one cation selected fromthe group consisting of cations of: Cr, Sb, Co, Ce and Pb; B is at leastone cation selected from the group consisting of cations of: Sb, Al andW; C is at least one cation selected from the group consisting ofcations of: Fe, Zn, Al, Sb, Bi, W, Li, Ba, Nb and Sn; E is at least onecation selected from the group consisting of cations of: Fe, Ca, Mn, Sr,Eu, La, Zr, Ga, Sn and Pb: and z, z′, z″, z′″, and z″″ are determinedusing the amounts and oxidation states of all cations present in eachformula according to the following equations: z=((q times oxidationstate of V)+(1 times oxidation state of Mo)+(y times oxidation state ofA)) divided by 2 (oxidation state of oxygen); z′=((1 times oxidationstate of Ni)+(x times oxidation state of Mo)+(y times oxidation state ofB)) divided by 2 (oxidation state of oxygen); z″=((1 times oxidationstate of V)+(w times the oxidation state of Ni)+(x times oxidation stateof Mo)+(y′ times oxidation state of C)) divided by 2 (oxidation state ofoxygen); and z″″=((1 times oxidation state of V)+(w times the oxidationstate of Ni)+(r times the oxidation state of Co)+(x times oxidationstate of Mo)+(y′ times oxidation state of E)) divided by 2 (oxidationstate of oxygen), to yield maleic anhydride.
 8. The process of claim 7wherein the molybdenum compound is of formula I and A is Sb.
 9. Theprocess of claim 7 wherein the molybdenum compound is of formula II andB is Sb.
 10. The process of claim 7 wherein the molybdenum compound isof formula III and C is Bi, or Nb and Sn.
 11. The process of claim 7wherein the molybdenum compound is of formula V and E is Fe, Sr, Zr, Gaor Pb.
 12. A process for the oxidation of n-butane to maleic anhydride,comprising: contacting n-butane with a source of oxygen in the presenceof a catalytic amount of a catalyst comprising a molybdenum compound offormula IV IV CoNi_(w)Mo_(x)D_(y)O_(z′″) wherein: w is a number from 0.1to 10; x is a number from 0.1 to 10; y is a number from 0.1 to 10; D isat least one cation selected from the group consisting of cations of:Ba, Mn, Al, Sb, Sn, and W; and z′″ is determined using the amounts andoxidation states of all cations present in formula IV according to thefollowing equation: z′″=((1 times oxidation state of Co)+(w times theoxidation state of Ni)+(x times oxidation state of Mo)+(y′ timesoxidation state of D)) divided by 2 (oxidation state of oxygen); whereinthe molybdenum compound is in the bulk state, to yield maleic anhydride.13. The process of claim 12 wherein D is Sn or W.
 14. A process for theoxidation of n-butane to maleic anhydride, comprising: contactingn-butane with a source of oxygen in the presence of a catalytic amountof a catalyst comprising a molybdenum compound of formula VI or VII in acrystalline, active phase VI V₉Mo₆O₄₀; VII V₂MoO₈; to yield maleicanhydride.
 15. A process for the preparation of a molybdenum compoundcomprising a molybdenum compound of formula I, II, III, IV or V: IV_(q)MoA_(y)O_(z) II NiMo_(x)B_(y)O_(z′) III VNi_(w)Mo_(x)C_(y′)O_(z″)IV CoNi_(w)Mo_(x)D_(y)O_(z′″) V VNi_(w)Co_(r)Mo_(x)E_(y)O_(″″) wherein:q is a number from 0.1 to 10; r is a number from 0.1 to 10; w is anumber from 0.1 to 10; x is a number from 0.1 to 10; y is a number from0.1 to 10; y′ is a number from 0 to 10, A is at least one cationselected from the group consisting of cations of: Cr, Sb, Co, Ce and Pb;B is at least one cation selected from the group consisting of cationsof: Sb, Al and W; C is at least one cation selected from the groupconsisting of cations of: Fe, Zn, Al, Sb, Bi, W, Li, Ba, Nb and Sn; D isat least one cation selected from the group consisting of cations of:Ba, Mn, Al, Sb, Sn, and W; E is at least one cation selected from thegroup consisting of cations of: Fe, Ca, Mn, Sr, Eu, La, Zr, Ga, Sn andPb; and z, z′, z″, z′″, and z″″ are determined using the amounts andoxidation states of all cations present in each formula according to thefollowing equations: z=((q times oxidation state of V)+(1 timesoxidation state of Mo)+(y times oxidation state of A)) divided by 2(oxidation state of oxygen); z′=((1 times oxidation state of Ni)+(xtimes oxidation state of Mo)+(y times oxidation state of B)) divided by2 (oxidation state of oxygen); z″=((1 times oxidation state of V)+(wtimes the oxidation state of Ni)+(x times oxidation state of Mo)+(y′times oxidation state of C)) divided by 2 (oxidation state of oxygen);z′″=((1 times oxidation state of Co)+(w times the oxidation state ofNi)+(x times oxidation state of Mo)+(y′ times oxidation state of D))divided by 2 (oxidation state of oxygen); and z″″=((1 times oxidationstate of V)+(w times the oxidation state of Ni)+(r times the oxidationstate of Co)+(x times oxidation state of Mo)+(y′ times oxidation stateof E)) divided by 2 (oxidation state of oxygen), comprising the stepsof: contacting at least one compound having a cation of the molybdenumcompound with at least one cation containing compound for each of theother cations of the molybdenum compound in a solution comprising waterto form a resultant solution or colloid; freezing the resultant solutionor colloid to form a frozen material; freeze drying the frozen material;and heating the dried frozen material to yield the molybdenum compoundof formula I, II, III, IV, V, VI or VII.